1. Field of the Invention
The present invention relates to a photoelectric encoder including a scale in which a grating is formed with a predetermined period, a light source and a light receiving unit which are movable relative to the scale. The present invention particularly relates to a photoelectric encoder suitable for use as a linear encoder and capable of reducing occurrence of a position detecting error due to stain on the scale or a defect of the grating through simple computing.
2. Description of the Related Art
Conventionally, a photoelectric encoder has been utilized for precisely measuring an amount of linear movement of an object to be measured. An arctangent calculation of Lissajous signals obtained from a light receiving element array is one of the position sensing methods often employed for an optical encoder.
In a method proposed in Japanese Patent Application Publication No. Sho 64-57120 (Patent Document 1), for example, firstly light receiving elements made of P-type semiconductor layers 34 respectively forming photosensitive zones 35 are arranged in an array at a pitch having a phase difference from the phase of an optical grating 12 of a scale 13, as shown in FIGS. 1 and 2 of Patent Document 1. Next, differential amplifiers 38A and 38B each amplify a difference between output signals from the light receiving elements to generate a Lissajous signal. Further, an arctangent calculation is performed on the Lissajous signals, so that a position is detected.